There are basically two types of helical scan video signal tape recording methods. One is the separated track method and the other is the "azimuth" recording method. In the separated track method, each track is arranged in parallel on a magnetic tape with a predetermined distance of space therebetween. This space between tracks is called a guard band and no signal is recorded thereon so that interference (crosstalk) between two tracks is avoided.
In the azimuth recording method, each track is positioned in parallel on the magnetic tape without a space, i.e. no guard band, where signals are recorded by arranging the azimuth of the two heads (gap orientation) in opposite directions with respect to the traverse direction of the track. Since a signal is recorded on an adjacent (next) track of a main track by a second head the gap orientation of which is different from that of the first head with which a signal is recorded on the main track, when reproducing, the signal recorded on the adjacent track is not effectively reproduced viz. very low output is obtained, by the first head due to the azimuth loss. This azimuth recording method is advantageous when the signal is reproduced at a normal tape speed since crosstalk between tracks is effectively reduced by using the correct (corresponding) head between two heads for each track. With the azimuth recording method, tape-saving is achieved since the tracks are positioned on a magnetic tape without any spaces.
Assuming a main track is recorded by a first head while an adjacent track is recorded by a second head by the azimuth recording method, when the signal is reproduced at a slow-motion tape speed, a signal recorded on the adjacent track is not effectively reproduced by the first head while the signal recorded on the main track is not effectively reproduced by the second head when the first and second heads respectively scan the main and adjacent tracks, because of the azimuth loss.
Since the first and second heads are arranged to alternatively scan a track or tracks, the above mentioned low output signal is obtained periodically. This undesirable low output causes the slow-motion picture on the picture tube to assume a poor quality. Therefore, the quality on the picture of the picture tube varies periodically.